1. Field of the Invention
The present invention relates to a peaking/depeaking circuit for accentuating the outlines of the objects in a television picture, or on the contrary, for attenuating the outlines. The present invention more particularly relates to a coring circuit for disabling the peaking when the level of the signal to process is too low.
2. Discussion of the Related Art
FIG. 1 is a functional diagram of a conventional peaking/depeaking circuit. In this circuit, a signal Y, generally a television luminance signal is delayed a first time by a delay circuit 10 and delayed a second time by a delay circuit 11. A circuit 13 provides a signal D2 that is twice the output Y2 of delay circuit 10 minus signal Y and the output Y3 of delay circuit 11. As indicated in FIG. 1, if signal Y is a square pulse, signal D2 has, at the beginning of the square pulse, a negative pulse immediately followed by a positive pulse and, at the end of the square pulse, a positive pulse immediately followed by a negative pulse.
Signal D2 is applied to the input of an attenuator 15, which multiplies signal D2 by a coefficient 0.125, and to the input of an attenuator 16 which multiplies signal D2 by a coefficient 0.375. The output DP of attenuator 15 is provided to a subtractor 18 which subtracts signal DP to the output of attenuator 16 which is previously processed by a coring circuit 20 and by a multiplier 22. The coring circuit 20 transmits at its output P the output signal of attenuator 16 only if this signal exceeds a predetermined level fixed by a coring signal C. Multiplier 22 multiplies the output P of the coring circuit 20 by a coefficient fixed by a gain signal G.
An adder 24 receives the output of subtractor 18 and the delayed luminance signal Y2, and provides the processed signal Yp.
Signal DP, which is a depeaking signal, is permanently subtracted from signal Y2, whereas signal P, which is a peaking signal, is more or less amplified, depending upon the gain signal G provided to multiplier 22, and added to signal Y2. If the multiplication coefficient of multiplier 22 is lower than 1/3, the subtraction of signal DP is dominant, and signal Yp has, as indicated in A, progressive step-form rising and falling edges. In contrast, if the multiplication coefficient of multiplier 22 exceeds 1/3, the addition of signal P is dominant. Then, signal Yp has, as indicated in B, a rising edge preceded by a negative pulse and followed by an overshot, and a falling edge preceded by an overshot and followed by a negative pulse.
Up to now, the functions of the block diagram of FIG. 1 have been achieved with elements operating in voltage mode.